I can also "just express my humble opinion based on some little design experience and few listening tests", I would rather use a discrete buffer stage than an op-amp. Some op-amps sound quite good but not one that I've tried, including the LM4562, could compare with the SQ of a discrete class A stage.

No worries Wavebourn. I'm fine with opinions--especially when it's a theoretical or philosophical discussion and there are no consequences involved. But when you factor in the DIY cost to spin PC boards, buy all the parts, all the time involved, etc. I try to steer fellow DIY'ers down the most ideal path possible. Most of us don't have unlimited time or budgets. And my personal preference, where possible, is to to offer suggestions I can back up with factual objective information and references.

Sadly, there are lots of myths perpetuated in high-end audio--some by very experienced individuals. Some myths have some truth behind them, some are pure fantasy, and with others we may never know. Those who say one solution is better or worse than another without providing any solid reasons just help perpetuate the myths despite many having little or no basis in fact. That's not sound engineering practice.

Personally, I hate to see someone go out and buy expensive op-amps, or hassle with a discrete design, when the outcome is likely to be no better--and more likely worse--than a much easier and less costly solution. And no, I have no affiliation in any way with National or current or former National employees beyond having a met a few of them at AES conferences, etc.

Originally posted by homemodder RocketScientist do you work for national or have any personal involvement or friendships with any one related to national ???.

You should rather say the audiophiles that national paid to review these chips liked them, dont forget there are many others that feel otherwise and from the looks of it theres quite a few and in the majority. I havent seen the national chips used in any top notch equipment this far, I have seen AD chips though but most opt for discretes. Its early days yet, well see how it goes in future.

Audio differencing is the exactly what I do, strangely I gather we get very different results. Well the only thing I can say in my defence is that I have no vested interest in any opamp company and evaluate purely on what my ears can hear. There will never be consensus corcerning these things but it would be interesting to see what well established and respected gurus like Nelson Pass, John Curl or Charles Hason would say about it.

And I have no interest in National (see my previous post). If AD comes out with a better chip, I'll start using those

There are way too many favorable reviews of products using the LM4562 for National to have paid them off. A good example are the many favorable reviews of the Benchmark Dac1 Pre which uses the LM4562 exclusively throughout the device. It's been rave reviewed by even Stereophile and the UK mags, as well as by several recording engineering mags on the pro side. Some have called the Dac1 Pre the best sounding DAC they've ever heard. If the Dac1 doesn't qualify as "top notch" by your standards, I'm sorry, but I think in terms of specs it's yet to be beat.

I do agree there will never be overall consensus about these sorts of things. But I, at least, have lots of favorable numbers and reviews on my side.

Originally posted by RocketScientist No worries Wavebourn. I'm fine with opinions--especially when it's a theoretical or philosophical discussion and there are no consequences involved. But when you factor in the DIY cost to spin PC boards, buy all the parts, all the time involved, etc. I try to steer fellow DIY'ers down the most ideal path possible. Most of us don't have unlimited time or budgets. And my personal preference, where possible, is to to offer suggestions I can back up with factual objective information and references.

The problem is, I myself and lot of other humble amateurs presented on this forum don't believe that THD measurement is the final criterion for audio, especially when THD goes up with lower output voltage swing, what you may clearly see on graphs of National's datasheet. However, I don't blame on National for that. I just expressed my humble opinion that if costs and sizes are not involved in optimization equations, opamps are suboptimal for audio amplifications.

The problem is, I myself and lot of other humble amateurs presented on this forum don't believe that THD measurement is the final criterion for audio, especially when THD goes up with lower output voltage swing, what you may clearly see on graphs of National's datasheet. However, I don't blame on National for that. I just expressed my humble opinion that if costs and sizes are not involved in optimization equations, opamps are suboptimal for audio amplifications.

As you hopefully know, the THD only rises because they're showing THD+N and, as the level drops, noise dominates the measurement rather than distortion. Regardless, even at extremely low levels, the THD+N of the LM4562 outperforms anything else I've ever seen used for audio. So it's a moot point.

And I agree THD is far from the only measurement of audio performance. The LM4562 excels at any measurement I'm aware of including transient tests, intermodulation distortion, noise, CMRR, PSRR, square waves, etc. And, ultimately, it also excels at playing real music as evidenced by audio difference testing and the many favorable listening reviews.

Also, I forgot to stress that THD goes up with frequency. I myself and several humble amateurs believe that it is also a very bad, counter-clear-audio symptom.

Virtually any amplifier with feedback applied exhibits rising distortion with frequency--even a fully class A discrete design. Even most open loop (non-feedback) amps exhibit some rise in distortion with frequency.

If you don't believe THD is important or especially audible, than it shouldn't matter if it rises or falls? If you do think THD is important and audible (as you suggest above), than I think it's important to quantify how much THD there is at high frequencies?

Here again, the LM4562 will beat nearly anything else at any frequency you want to pick in terms of THD. So are you saying you'd rather have say an open loop class A design that at any frequency likely has literally 1000 times as much THD as the LM4562 but the high level of distortion rises less at high frequencies? If so, please explain how that is better?

And if you have an example of a very low distortion line-level audio amp that doesn't rise with frequency, please provide a reference?

If you don't believe THD is important or especially audible, than it shouldn't matter if it rises or falls? If you do think THD is important and audible (as you suggest above), than I think it's important to quantify how much THD there is at high frequencies?

Dear Rocket Scientist;
I did not say that I don't believe that THD is important and especially audible; I just expressed my humble opinion that it is not the single final criterion that may be used to compare solutions. But it may be used as a symptom in case of absence of other facts. Also, I believe that there is one and only one way to reproduce clean sound, while number of ways to distort it is countless. That's why more and more of measurement methods are being invented, but they still can't cover all errors that may be created. It reminds me a crowd of persons that instead of going to the goal always try to avoid obstacles, so always have to back up bumping into walls, trees, poles, each other, falling in holes, and so on, because concentrating on problems (distortions), running from them backward, that crowd of smart persons don't see what is behind.

Quote:

And if you have an example of a very low distortion line-level audio amp that doesn't rise with frequency, please provide a reference?

May I ask you please, to follow the link that I posted before? There I described the concept of a buffer that I used in a hybrid power amp, in a class A+C amp driver, and in line level output stages. I would appreciate if you express your educated scientific opinion about it.

Actually, it is a source follower that is bootstrapped on top in order to keep a voltage between source and drain stable, non-modulated by an amplified signal. Also, it is loaded on current source that is modulated by an input signal, in counter - phase. As the result, the source follower exhibits the lowest possible distortions without any additional negative feedback that may create multiple distortions that were already caught, and other distortions that may be caught up in the future by scientists and engineers who are still curious why all known measurements don't correlate with listening tests, and what kind of errors must be measured to understand why they still don't correlate, instead of an usual excuse that people who claim to hear distortions are crazy.

Edit: "additional" word was added for strictness of expression of my humble opinion.

May I ask you please, to follow the link that I posted before? There I described the concept of a buffer that I used in a hybrid power amp, in a class A+C amp driver, and in line level output stages. I would appreciate if you express your educated scientific opinion about it.

I followed the link the first time, thanks. I don't consider it an example of anything Oystein might want to use in his pre-amp. And, trying to be polite, I didn't think you would appreciate my opinion of the "Tower-III" power amp so I thought it better to say nothing. I will, however, buy you a very nice dinner if the line stage has less distortion than an LM4762. It appears to be a rather unique design--at least to my eyes.

But it's not an example, in my opinion, of something superior to the LM4762--at least by any objective measure. And it's also a safe bet it has distortion that rises at high frequencies like virtually every other audio amplifier--including the $10,000 and up models so loved by the audiophile press.

If you honestly want more of an opinion, I'm probably not the best person to ask as I don't personally do much with tube or hybrid tube designs. I'm not a big fan of their almost always higher and often audible distortion--euphonic or otherwise.

But I also recognize lots of guys like how tubes sound and I respect that. Some of us like our audio signal as uncorrupted as possible and others like to pour ketchup on their $40 steak because it tastes better to them that way. It's ultimately about what puts the biggest smile on your face while listening to music.